Dental impression trays serve to receive a curable material to obtain an impression of a patient's tooth or teeth. By filling the impression, e.g. with gypsum or other materials, a model of the tooth or teeth can be produced which may serve as the working basis for the dental technician.
The precision of the impression is of critical importance for producing high-quality, well fitting dental replacement parts.
Known in the art are impression trays of metal and of synthetic material. Both are widely in use.
Due to the varying sizes and geometries of the human jaws and depending on the specific application, a plurality of tray sizes and shapes, often sold in sets, must be available. Further, since the most frequently needed trays are most frequently with the technician, a plurality of sets of trays must be available to the dentist.
Impression trays of metal are of advantage as their high rigidity and dimensional stability permits the production of very exact impressions and models, from which very exactly fitting dental replacement parts can be prepared. Due to the necessity of having a plurality of sets of trays, the use of metal trays involves high costs. In view of the high costs, the dentist is further faced with the inconvenience of having to control the return of the metal trays from the technician or dental laboratory. In addition, the dentist has to provide for suitable storage of metal trays upon their sterilization to exclude contamination until their reuse.
Another essential disadvantage of metal impression trays resides in the fact that they cannot be individualized. In contrast to trays of materials such as synthetic resin, which can be worked easily, metal trays are unsuited for adapting the tray geometry to the anatomy of an individual patient.
Impression trays of synthetic material, on the other hand, involve low cost and therefore permit disposal. They further allow the cured model to be removed by destroying the tray, which may be useful with certain impressions, e.g., in the case of undercuts, in order to save the model. Furthermore, there is no sterilization and subsequent clean storage. However, the relatively low mechanical strength and dimensional stability of trays made of synthetic material may lead to deformations of the impression while taken. Models prepared from a deformed impression are less accurate and thus of lower quality. If the dimensions of the model differ from those of the teeth from which it was taken, imperfect fitting of the finished dental replacement part will result even if the technician has worked meticulously from the model. In such a case, post-treatment by the dentist will be necessary, if at all possible, and the patient will end up with a dental replacement part that does not fit completely.
German Offenlegungsschrift 196 28 682 discloses a reusable metallic dental impression tray made of several parts that can be disassembled to simplify the removal of the cured impression material.
German Patent Specification 4131 145 shows a dental impression tray made of metal with a thin, flexible insert made of plastic material. Both parts cooperate to receive the impression material and form retentions therefor. Since the flexible insert has virtually no rigidity of its own, it must be supported on all sides by the outer tray.